The reason they allowed it near Kharkiv is because Russia has their military stuff parked pretty much out in the open in plain sight on their side of the border knowing full well there’s nothing Ukraine can do about it. They’re doing constant cross-border raids and cheap glide bombs are especially a problem as they can drop them from a high altitude 20km behind the borders without ever entering Ukrainian air space. That is not so much of an issue on the eastern front because the territory where most of the Russians are is already in Ukraine. Same as with Crimea.